The present invention relates to metallurgy and, more particularly, to an improved method for measuring the temperature of a metallurgical furnace.
Russian Patent No. 2,006,007, which is incorporated by reference for all purposes as if fully set forth herein, describes a method for measuring the temperature of a metallurgical furnace such as a blast furnace. The acoustic noise spectrum of the furnace is measured. The frequency F of maximum acoustic noise power is determined from the spectrum. The temperature is determined by an equation of the form ##EQU1## where L is an estimated wavelength of acoustic noise in the furnace, K is the adiabatic exponent of the gas in the furnace, for example, carbon monoxide in a blast oxygen steel furnace, and R is the gas constant. The wavelength L is estimated from the rate of oxygen consumption of the furnace, using an empirical calibration based on explicit measurements of T, F, the rate of oxygen consumption, and parameters, such as the Mach number, of the nozzle used to inject the oxygen.
In practice, it has proven difficult to implement this method, because of the difficulty of picking the frequency of maximum acoustic noise power in real time. FIG. 1 shows a typical acoustic noise spectrum of a blast oxygen steel furnace. The abscissa is frequency, in Hertz, and the ordinate is the output of a digital spectrum analyzer, in millivolts. The ordinate is proportional to the acoustic noise power at each frequency. The portion of the spectrum that corresponds to the noise generated by the injection of oxygen into the furnace is the portion between 300 Hertz and 1400 Hertz. Note that the spectrum is far from a smooth function of frequency. Although, strictly speaking, there is in fact a frequency of maximum power in this range, the position of this maximum changes unpredictably from measurement to measurement in a way that is not reflected in the temperature of the furnace.
FIG. 2 shows an acoustic noise spectrum recorded similarly for an electric arc furnace. In this case, it is impossible to pick a frequency of maximum power.